In recent years, new federal laws require that most vehicles be outfitted with Tire Pressure Monitoring Systems (TPMS) by Sep. 1, 2007. There are two basic types of TPMS: indirect, and direct.
Indirect TPMS use a vehicle's existing Anti-lock Braking System (ABS) to monitor and compare the rotational speed of each road wheel. The indirect TPMS infers over-inflation if the rotational speed appears too low (due to a large diameter of an over-inflated wheel), and infers under-inflation if the rotational speed appears too high (due to a small diameter of an under-inflated wheel). Indirect TPMS are relatively inexpensive because they utilize pre-existing ABS sensors to infer over-inflation or under-inflation.
Unfortunately, the indirect TPMS is unable to detect tire deflation of typically less than 30%. Also, tire changes require resetting the system to relearn the dynamic relationship between wheels, creating lifetime maintenance and calibration issues. And, because the system makes differential measurements, it can not independently treat each wheel. Indirect TPMS cannot detect a case in which all four tires are under-inflated to a similar degree, which can easily occur with similar tires over an extended period of neglect. For these reasons, indirect TPMS systems have fallen out of favor.
Direct Tire Pressure Monitoring Systems (TPMS) are relatively expensive because they require additional hardware and software in the vehicle: However, direct TPMS systems are more accurate because they directly and individually measure the pressure of every tire. For example, direct TPMS systems are capable of generating a driver warning when any or all of the tires fall 20% below the manufacturer's recommended cold-inflation pressures. Additionally, direct TPMS may simultaneously directly measure tire temperatures, and thus may compensate for cold-to-warm-running tire-pressure changes and for temperature dependencies within the pressure sensors. For these reasons, direct TPMS appear to be the only systems that will satisfy the strict requirements of new federal regulations.
Typically, a tire sensor is built into a valve stem of a tire, and may transmit information such as a sensor identification (ID), pressure, temperature, battery status, and error codes to a vehicle control module. The tire sensor (or tire pressure monitoring sensor) typically comprises a battery, a communication antenna, a pressure sensor, and a memory for storing a sensor identification.
The tire sensor battery is physically small, and accordingly has a corresponding small energy storage capacity. To maximize the life of the battery, the tire sensor conserves energy by “sleeping” (not measuring pressure or temperature, and not transmitting information) until it receives an triggering signal. For example, a vehicle may send one triggering signal after the engine has been started, and send a second triggering signal after the car has been moving for 5 minutes. After receiving a triggering signal, the tire sensor may measure pressure and temperature, and then transmit the pressure, the temperature, and a sensor ID to a vehicle control module or TPMS of a vehicle. After transmitting, the tire sensor may return to sleep in order to conserve battery energy. Triggering formats include continuous wave, modulated pulse, and magnetic. Different sensor manufacturers may use different triggering formats.
Using unique sensor IDs allows the TPMS to identify a specific tire, and to ignore tires from other cars. A vehicle may have an instrument cluster display (or a vehicle tire pressure monitoring system display) that displays tire positions. The vehicle must be trained or programmed with the position of each specific tire. For example, tire ID 123 may be located at the front left tire location. A tire pressure monitoring tool is used to trigger the tire sensor to transmit the tire ID 123, and thus train the vehicle that the tire with ID 123 is located at the front left position.
Typically, during training the front left tire sensor is triggered first, then the right front tire sensor, next the right rear tire sensor, and finally the left rear tire sensor. Some vehicles also train the spare tire between the right rear and the left rear. Each time that a tire is changed, or a tire position is changed (such as tire rotation), the TPMS must be retrained.
A current conventional tire pressure monitoring tool utilizes six AA size batteries for power to trigger the tire sensor. The conventional tool must be partially disassembled to access and remove the AA batteries for replacement. For example, the Snap-on® Tire Pressure Monitoring System Tool model TPMS 1 uses six AA size batteries. Performance of the tool may degrade as the batteries run down.
Additionally, new tire sensors may require new triggering procedures, and the conventional tool should be regularly updated with new software containing the new triggering procedures. The conventional tool requires a complex procedure to update the programming or software. The complex procedure typically requires following steps: (1) the pressure monitoring tool is partially disassembled by removing an access plate and a battery pack to access an internal communication port; (2) the first end of a first communication line is manually inserted to the internal communication port; (3) the second end of the first communication line is inserted into a programming interface module (PIM); (4) the programming interface module is connected with a second communication line to a computer with Internet access; (5) a mechanic uses the computer to log into an Internet website; (6) if necessary, additional licenses are purchased by the mechanic from an appropriate Internet site; (7) appropriate software is downloaded to the pressure monitoring tool; (8) both communication cables and are disconnected; (9) the battery pack is replaced inside the tool; (10) the access plate is replace on the tool; (11) the programming interface module is stored; and (12) both communication cables are stored for future use.
Unfortunately, the conventional tool is merely a triggering device. The conventional tool merely transmits a triggering signal to the sensor, and the sensor transmits a reporting signal to the a vehicle control module or TPMS of a vehicle. At best, some models of the conventional tool may recognize that a reporting signal has been transmitted by the sensor. Thus, the conventional tool is limited to triggering the sensor for the purpose of training regarding sensor location, but cannot extract, store, and output data from the reporting signal.
Specifically, the conventional tool disadvantageously does not extract data from the reporting signal, does not store the extracted data from the reporting signal, and does not communicate the stored data to an external device.